Liquid-crystal medium

ABSTRACT

The invention relates to a liquid-crystalline medium of negative dielectric anisotropy based on a mixture of polar compounds, which comprises at least one compound selected from the group of the compounds of the formulae IA, IB and IC 
                         
in which
     R 1A , R 2A , R 1B , R 2B , R 1C , R 2C , L, m, n, o, p and b have the meanings indicated in Claim  1,      and to the use thereof for an active-matrix display, in particular based on the ECB, PALC, FFS or IPS effect.

The invention relates to a liquid-crystalline medium of negativedielectric anisotropy based on a mixture of polar compounds, whichcomprises at least one compound selected from the group of the compoundsof the formulae IA, IB and IC

in which

-   R^(1A), R^(1B),-   R^(2B) and R^(1C) each, independently of one another, denote an    alkyl radical having 2-6 C atoms,-   R^(2A) and R^(2C) each, independently of one another, denote an    alkyl radical having up to 6 C atoms which is unsubstituted,    mono-substituted by CN or CF₃ or at least monosubstituted by    halogen, where, in addition, one or more CH₂ groups in these    radicals may be replaced by —O—, —S—,

—C≡C—, —CF₂O—, —OCF₂—, —OC—O— or —O—CO— in such a way that O atoms arenot linked directly to one another, and, if L=F, R^(2C) may also denotehalogen, preferably F or Cl,

-   L denotes H or F,-   m, n, o and p each, independently of one another, denote 0, 1 or 2,-   b denotes 0 or 1.

Media of this type can be used, in particular, for electro-opticaldisplays having active-matrix addressing based on the ECB effect and forIPS (in-plane switching) displays and FFS (fringe field switching)displays. The medium according to the invention preferably has negativedielectric anisotropy.

The principle of electrically controlled birefringence, the ECB effector also DAP (deformation of aligned phases) effect, was described forthe first time in 1971 (M. F. Schieckel and K. Fahrenschon, “Deformationof nematic liquid crystals with vertical orientation in electricalfields”, Appl. Phys. Lett. 19 (1971), 3912). This was followed by papersby J. F. Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J.Robert (J. Appl. Phys. 44 (1973), 4869).

The papers by J. Robert and F. Clerc (SID 80 Digest Techn. Papers(1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82Digest Techn. Papers (1982), 244) showed that liquid-crystalline phasesmust have high values for the ratio of the elastic constants K₃/K₁, highvalues for the optical anisotropy Δn and values for the dielectricanisotropy of Δ∈≦−0.5 in order to be suitable for use inhigh-information display elements based on the ECB effect.Electro-optical display elements based on the ECB effect have ahomeotropic edge alignment (VA technology=vertically aligned).Dielectrically negative liquid-crystal media can also be used indisplays which use the so-called IPS or FFS effect.

Displays which use the ECB effect, as so-called VAN (vertically alignednematic) displays, for example in the MVA (multi-domain verticalalignment, for example: Yoshide, H. et al., paper 3.1: “MVA LCD forNotebook or Mobile PCs . . . ”, SID 2004 International Symposium, Digestof Technical Papers, XXXV, Book I, pp. 6 to 9, and Liu, C. T. et al.,paper 15.1: “A 46-inch TFT-LCD HDTV Technology . . . ”, SID 2004International Symposium, Digest of Technical Papers, XXXV, Book II, pp.750 to 753), PVA (patterned vertical alignment, for example: Kim, SangSoo, paper 15.4: “Super PVA Sets New State-of-the-Art for LCD-TV”, SID2004 International Symposium, Digest of Technical Papers, XXXV, Book II,pp. 760 to 763), ASV (advanced super view, for example: Shigeta,Mitzuhiro and Fukuoka, Hirofumi, paper 15.2: “Development of HighQuality LCDTV”, SID 2004 International Symposium, Digest of TechnicalPapers, XXXV, Book II, pp. 754 to 757) modes, have establishedthemselves as one of the three more recent types of liquid-crystaldisplay that are currently the most important, in particular fortelevision applications, besides IPS (inplane switching) displays (forexample: Yeo, S. D., paper 15.3: “An LC Display for the TV Application”,SID 2004 International Symposium, Digest of Technical Papers, XXXV, BookII, pp. 758 & 759) and the long-known TN (twisted nematic) displays. Thetechnologies are compared in general form, for example, in Souk, Jun,SID Seminar 2004, Seminar M-6: “Recent Advances in LCD Technology”,Seminar Lecture Notes, M-6/1 to M-6/26, and Miller, Ian, SID Seminar2004, Seminar M-7: “LCD-Television”, Seminar Lecture Notes, M-7/1 toM-7/32. Although the response times of modern ECB displays have alreadybeen significantly improved by addressing methods with overdrive, forexample: Kim, Hyeon Kyeong et al., paper 9.1: “A 57-in. Wide UXGATFT-LCD for HDTV Application”, SID 2004 International Symposium, Digestof Technical Papers, XXXV, Book I, pp. 106 to 109, the achievement ofvideo-compatible response times, in particular on switching of greyshades, is still a problem which has not yet been satisfactorily solved.

Industrial application of this effect in electro-optical displayelements requires LC phases, which have to satisfy a multiplicity ofrequirements. Particularly important here are chemical resistance tomoisture, air and physical influences, such as heat, infrared, visibleand ultraviolet radiation and direct and alternating electric fields.

Furthermore, industrially usable LC phases are required to have aliquid-crystalline mesophase in a suitable temperature range and lowviscosity.

None of the hitherto-disclosed series of compounds having aliquid-crystalline mesophase includes a single compound which meets allthese requirements. Mixtures of two to 25, preferably three to 18,compounds are therefore generally prepared in order to obtain substanceswhich can be used as LC phases. However, it has not been possible toprepare optimum phases easily in this way since no liquid-crystalmaterials having significantly negative dielectric anisotropy andadequate long-term stability were hitherto available.

Matrix liquid-crystal displays (MLC displays) are known. Non-linearelements which can be used for individual switching of the individualpixels are, for example, active elements (i.e. transistors). The term“active matrix” is then used, where a distinction can be made betweentwo types:

-   1. MOS (metal oxide semiconductor) transistors on a silicon wafer as    substrate-   2. thin-film transistors (TFTs) on a glass plate as substrate.

In the case of type 1, the electro-optical effect used is usuallydynamic scattering or the guest-host effect. The use of single-crystalsilicon as substrate material restricts the display size, since evenmodular assembly of various part-displays results in problems at thejoints.

In the case of the more promising type 2, which is preferred, theelectro-optical effect used is usually the TN effect.

A distinction is made between two technologies: TFTs comprising compoundsemiconductors, such as, for example, CdSe, or TFTs based onpolycrystalline or amorphous silicon. The latter technology is beingworked on intensively worldwide.

The TFT matrix is applied to the inside of one glass plate of thedisplay, while the other glass plate carries the transparentcounterelectrode on its inside. Compared with the size of the pixelelectrode, the TFT is very small and has virtually no adverse effect onthe image. This technology can also be extended to fully colour-capabledisplays, in which a mosaic of red, green and blue filters is arrangedin such a way that a filter element is opposite each switchable pixel.

The TFT displays disclosed hitherto usually operate as TN cells withcrossed polarisers in transmission and are back-lit.

The term MLC displays here covers any matrix display with integratednon-linear elements, i.e. besides the active matrix, also displays withpassive elements, such as varistors or diodes(MIM=metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications(for example pocket TVs) or for high-information displays in automobileor aircraft construction. Besides problems regarding the angledependence of the contrast and the response times, difficulties alsoarise in MLC displays due to insufficiently high specific resistance ofthe liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H.,YAMAMOTO, E., SORI-MACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H.,Proc. Eurodisplay 84, September 1984: A 210-288 Matrix LCD Controlled byDouble Stage Diode Rings, pp. 141 ff., Paris; STROMER, M., Proc.Eurodisplay 84, September 1984: Design of Thin Film Transistors forMatrix Addressing of Television Liquid Crystal Displays, pp. 145 ff.,Paris]. With decreasing resistance, the contrast of an MLC displaydeteriorates. Since the specific resistance of the liquid-crystalmixture generally drops over the life of an MLC display owing tointeraction with the inside surfaces of the display, a high (initial)resistance is very important for displays that have to have acceptableresistance values over a long operating period.

The disadvantages of the MLC-TN displays disclosed hitherto are theircomparatively low contrast, the relatively high viewing-angle dependenceand the difficulty of producing grey shades in these displays.

There thus continues to be a great demand for MLC displays having veryhigh specific resistance at the same time as a large working-temperaturerange, short response times and a low threshold voltage with the aid ofwhich various grey shades can be produced.

For television applications in particular, it is a very important toachieve short response times. In order to achieve this, thedielectrically neutral compounds used in ECB applications are, inparticular, compounds of the formulae

In LCD television applications, reliability problems frequently occurs,such as, for example, image sticking, i.e. apparent “burning-in” of theimage if the display has been addressed over an extended time.

This problem frequently only occurs after extended running times of thetelevision sets. The cause is frequently regarded as being the longexposure time to the backlight at the same time as increased operatingtemperatures, which can result in still unexplained processes in thedisplay, for example an interaction between alignment layer and aliquid-crystal mixture. On the part of the liquid-crystal mixture, thecause of the occurrence of image sticking is regarded as being theneutral alkenyl compounds frequently used.

The invention is based on the object of providing liquid-crystalmixtures, in particular for monitor and TV applications, which are basedon the ECB effect or on the IPS or FFS effect, which do not have theabove-mentioned disadvantages or only do so to a reduced extent. Inparticular, it must be ensured for monitors and televisions that theyalso operate at extremely high and extremely low temperatures and at thesame time have short response times and at the same time have improvedreliability behaviour, in particular have no or significantly reducedimage sticking after long operating times.

Surprisingly, it has now been found that this object can be achieved ifnematic liquid-crystal mixtures which comprise at least one compoundfrom the group of the compounds of the formulae IA, IB and IC are usedin these display elements.

The compounds of the formulae IA, IB and IC are distinguished by thefact that the double bond in the alkenyl side chain is not terminal.

Compounds of the formula IA are known, for example, from EP 0 168 683 B1and EP 0 122 389 B1. The compounds of the formula IB are known, forexample, from EP 0 969 071 B1. The compounds of the formula IC areknown, for example, from EP 0 969 071 B1.

The invention thus relates to a liquid-crystalline medium based on amixture of polar compounds which comprises at least one compoundselected from the group of the compounds of the formulae IA, IB, IC.

The mixtures according to the invention preferably exhibit very broadnematic phase ranges with clearing points ≧60° C., preferably ≧65° C.,in particular ≧70° C., very favourable values for the capacitivethreshold, relatively high values for the holding ratio and at the sametime very good low-temperature stabilities at −30° C. and −40° C. aswell as very low rotational viscosities and short response times. Themixtures according to the invention are furthermore distinguished by thefact that, in addition to the improvement in the rotational viscosityγ₁, an increase in the elastic constant K₃₃ for improving the responsetimes can be observed, and exhibit improved reliability behaviour.

Some preferred embodiments of the mixtures according to the inventionare given below:

-   a) R^(1A), R^(1B), R^(2B) and R^(1C) in the formulae IA, IB and IC    preferably denote straight-chain alkyl, in particular C₂H₅, n-C₃H₇,    n-C₄H₉, furthermore n-C₅H₁₁, n-C₆H₁₃.    -   R^(2A) and R^(2C) preferably denote alkyl or alkoxy, in        particular CH₃, n-C₃H₇, n-C₅H₁₁, furthermore C₂H₅, n-C₄H₉.    -   The alkenyl side chains in the compounds of the formulae IA, IB        and IC are preferably in the E configuration.-   b) Liquid-crystalline medium which comprises one, two, three, four    or more, preferably one, two or three, compounds of the formulae IA,    IB and/or IC,-   c) Liquid-crystalline medium in which the proportion of compounds of    the formula IA in the mixture as a whole is ≧5% by weight,    preferably at least 10% by weight, particularly preferably ≧15% by    weight.    -   The proportion of compounds of the formula IB in the mixture as        a whole, if present, is preferably ≧5% by weight, in particular        ≧10% by weight, very particularly preferably ≧20% by weight.    -   The proportion of compounds of the formula IC in the mixture as        a whole, if present, is preferably ≧2% by weight, in particular        ≧4% by weight, very particularly preferably ≧5% by weight.    -   The total proportion of the compounds of the formulae IA, IB        and/or IC in the mixture according to the invention is        preferably ≧5% by weight, in particular ≧10% by weight and very        particularly preferably ≧15% by weight.-   d) Preferred compounds of the formulae IA, IB and IC are the    compounds of the formulae:

-   -   Particularly preferred compounds are the compounds of the        formulae IA-1 and IC-1.    -   Very particularly preferred compounds of the formula IA are the        compounds

-   -   Preferred mixtures comprise a compound of the formula

-   -   in combination with a compound of the formula

-   -   preferably each in concentrations of 5-15% by weight.    -   Preferred mixtures comprise a compound of the formula

-   -   in combination with a compound of the formula

-   -   preferably each in concentrations of 5-15% by weight.

-   e) Liquid-crystalline medium which additionally comprises one or    more compounds of the formulae IIA and/or IIB

-   -   in which

-   R² denotes H, an alkyl radical having up to 15 C atoms which is    unsubstituted, monosubstituted by CN or CF₃ or at least    monosubstituted by halogen, where, in addition, one or more CH₂    groups in these radicals may be replaced by —O—, —S—,

—C≡C—, —CF₂O—, —OCF₂—, —OC—O— or —O—CO— in such a way that O atoms arenot linked directly to one another,

-   -   L¹⁻⁴ each, independently of one another, denote F or Cl,    -   Z² and Z^(2′) each, independently of one another, denote a        single bond, —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,        —COO—, —OCO—, —C₂F₄—, —CF═CF—, —CH═CHCH₂O—,    -   p denotes 1 or 2, and    -   v denotes 1 to 6.    -   In the compounds of the formulae IIA and IIB, Z² may have        identical or different meanings.    -   In the compounds of the formulae IIA and IIB, R² preferably        denotes alkyl having 1-6 C atoms, in particular straight-chain        alkyl, preferably CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁.    -   In the compounds of the formulae IIA and IIB, L¹, L², L³ and L⁴        preferably denote L¹=L²=F and L³=L⁴=F, furthermore L¹=F and        L²=Cl, L¹=Cl and L²=F. L³=F and L⁴=Cl, L³=Cl and L⁴=F. Z² and        Z^(2′) in the formulae IIA and IIB preferably each,        independently of one another, denote a single bond, furthermore        a —C₂H₄— bridge.    -   If Z²=—C₂H₄— in the formula IIB, Z^(2′) is preferably a single        bond or, if Z^(2′)=—C₂H₄—, Z² is preferably a single bond. In        the compounds of the formulae IIA and IIB, (O)C_(v)H_(2v+1)        preferably denotes OC_(v)H_(2v+1), furthermore C_(V)H_(2v+1).    -   Preferred compounds of the formulae IIA and IIB are mentioned        below.

-   -   In the compounds of the formulae IIA and IIB, R² in each case        preferably denotes straight-chain alkyl having up to 6 C atoms,        in particular CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁. L¹⁻⁴        preferably each denote F.    -   The proportion of compounds of the formulae IIA and/or IIB in        the mixture as a whole is preferably at least 20% by weight.

-   f) Liquid-crystalline medium which additionally comprises one or    more compounds of the formula III

-   -   in which    -   R³¹ and R³² each, independently of one another, denote a        straight-chain alkyl, alkoxyalkyl or alkoxy radical having up to        12 C atoms, and

-   -   Z³ denotes a single bond, —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—,        —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —C₄H₈—, —CF═CF—.    -   Preferred compounds of the formula III are mentioned below:

-   -   in which    -   alkyl and    -   alkyl* each, independently of one another, denote a        straight-chain alkyl radical having 1-6 C atoms.    -   The medium according to the invention preferably comprises at        least one compound of the formula IIIa, formula IIIb and/or        formula IIId.    -   The proportion of compounds of the formula III in the mixture as        a whole is preferably at least 5% by weight.

-   g) Liquid-crystalline media comprising a compound of the formula

and/or

and/or

-   -   preferably in total amounts of <20% by weight, in particular        <10% by weight.    -   Preference is furthermore given to mixtures according to the        invention comprising the compound

-   h) Liquid-crystalline medium which additionally comprises one or    more tetracyclic compounds of the formulae

-   -   in which    -   R⁷⁻¹⁰    -   each, independently of one another, have one of the meanings        indicated for R² in Claim 2, and    -   w and x each, independently of one another, denote 1 to 6.

-   i) Liquid-crystalline medium which additionally comprises one or    more compounds of the formulae Y-1 to Y-6

-   -   in which R¹³-R¹⁸ each, independently of one another, denote an        alkyl or alkoxy radical having 1-6 C atoms; z and m each,        independently of one another, denote 1-6; x denotes 0, 1, 2 or        3.    -   The medium according to the invention particularly preferably        comprises one or more compounds of the formulae Y-1 to Y-6 in        amounts of ≧5% by weight.

-   j) Liquid-crystalline medium which additionally comprises one or    more compounds of the formula

-   -   preferably in amounts of >3% by weight, in particular ≧5% by        weight, and very particularly preferably 5-25% by weight,    -   where    -   R¹⁹ denotes alkyl or alkoxy having 1-7 C atoms.

-   k) Liquid-crystalline medium additionally comprising one or more    fluorinated terphenyls of the formulae T-1 to T-21

-   -   in which    -   R denotes a straight-chain alkyl or alkoxy radical having 1-7 C        atoms, and m is 1-6.    -   R preferably denotes methyl, ethyl, propyl, butyl, pentyl, hexyl        methoxy, ethoxy, propoxy, butoxy, pentoxy.    -   The medium according to the invention preferably comprises the        terphenyls of the formulae T-1 to T-21 in amounts of 2-30% by        weight, in particular 5-20% by weight.    -   Particular preference is given to compounds of the formulae T-1,        T-2, T-3 and T-21. In these compounds, R preferably denotes        alkyl, furthermore alkoxy, each having 1-5 C atoms.    -   Particularly preferred media according to the invention        comprising a compound of the formula

-   -   in which alkyl and alkyl* have the meanings indicated above.    -   The terphenyls are preferably employed in the mixtures according        to the invention if the Δn value of the mixture is intended to        be ≧0.1. Preferred mixtures comprise 2-20% by weight of one or        more terphenyl compounds selected from the group of the        compounds T-1 to T-21.

-   l) Liquid-crystalline medium additionally comprising one or more    biphenyls of the formulae B-1 to B-3

-   -   in which    -   alkyl and alkyl* each, independently of one another, denote a        straight-chain alkyl radical having 1-6 C atoms, and    -   alkenyl and alkenyl* each, independently of one another, denote        a straight-chain alkenyl radical having 2-6 C atoms.    -   The proportion of the biphenyls of the formulae B-1 to B-3 in        the mixture as a whole is preferably at least 3% by weight, in        particular ≧5% by weight.    -   Of the compounds of the formulae B-1 to B-3, the compounds of        the formula B-2 are particularly preferred.    -   Particularly preferred biphenyls are

-   -   in which alkyl* denotes an alkyl radical having 1-6 C atoms. The        medium according to the invention particularly preferably        comprises one or more compounds of the formulae B-1a and/or        B-2c.

-   m) Liquid-crystalline medium comprising at least one compound of the    formulae Z-1 to Z-7

-   -   in which R and alkyl have the meanings indicated above.

-   n) Liquid-crystalline medium comprising a least one compound of the    formulae O-1 to O-15

-   -   in which R¹ and R² have the meanings indicated for R^(2A), R¹        and R² preferably each, independently of one another, denote        straight-chain alkyl.    -   Preferred media comprise one or more compounds of the formulae        O-1, O-3, O-4, O-9, O-13, O-14 and/or O-15.

-   o) Preferred liquid-crystalline media according to the invention    comprise one or more substances which contain a tetrahydronaphthyl    or naphthyl unit, such as, for example, the compounds of the    formulae N-1 to N-5

-   -   in which R^(1N) and R^(2N) each, independently of one another,        have the meanings indicated for R^(2A), preferably denote        straight-chain alkyl, straight-chain alkoxy or straight-chain        alkenyl, and Z¹ and Z² each, independently of one another,        denote    -   —C₂H₄—, —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CHCH₂CH₂—,        —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —CF═CF—,        —CF═CH—, —CH═CF—, —CF₂O—, —OCF₂—, —CH₂— or a single bond.

-   p) Preferred mixtures comprise one or more compounds selected from    the group of the difluorodibenzochroman compounds of the formula BC,    chromans of the formula CR, fluorinated phenanthrenes of the    formulae PH-1 and PH-2, fluorinated dibenzofurans of the formula BF,

-   -   in which    -   R^(B1), R^(B2), R^(CR1), R^(CR2) R¹, R² each, independently of        one another, have the meaning of R^(2A). c is 0, 1 or 2. The        mixtures according to the invention preferably comprise the        compounds of the formulae BC, CR, PH-1, PH-2 and/or BF in        amounts of 3 to 20% by weight, in particular in amounts of 3 to        15% by weight.    -   Particularly preferred compounds of the formulae BC and CR are        the compounds BC-1 to BC-7 and CR-1 to CR-5

-   -   in which    -   alkyl and alkyl* each, independently of one another, denote a        straight-chain alkyl radical having 1-6 C atoms, and    -   alkenyl and    -   alkenyl* each, independently of one another, denote a        straight-chain alkenyl radical having 2-6 C atoms.    -   Very particular preference is given to mixtures comprising one,        two or three compounds of the formula BC-2.

-   q) Preferred mixtures comprise one or more indane compounds of the    formula In

-   -   in which    -   R¹¹, R¹²,    -   R¹³ denote a straight-chain alkyl or alkoxy, alkoxyalkyl or        alkenyl radical having 1-5 C atoms,    -   R¹² and R¹³ additionally denote halogen, preferably F,

-   -   i denotes 0, 1 or 2.    -   Preferred compounds of the formula In are the compounds of the        formulae In-1 to In-16 given below:

-   -   Particular preference is given to the compounds of the formulae        In-1, In-2, In-3.

The compounds of the formula In and of the sub-formulae In-1 to In-16are preferably employed in concentrations ≧5% by weight, in particular5-30% by weight and very particularly preferably 5-25% by weight, in themixtures according to the invention.

-   r) Preferred mixtures comprise one or more compounds of the formulae    L-1 to L-11

-   -   in which    -   R, R¹ and R² each, independently of one another, have the        meanings indicated for R^(2A) in Claim 1, and alkyl denotes an        alkyl radical having 1-6 C atoms. S denotes 1 or 2.    -   Particular preference is given to the compounds of the formulae        L-1 and L-4.    -   The compounds of the formulae L-1 to L-10 are preferably        employed in concentrations of 5-50% by weight, in particular        5-40% by weight and very particularly preferably 10-40% by        weight.

The invention furthermore relates to an electro-optical display havingactive-matrix addressing based on the ECB, IPS or FFS effect,characterised in that it contains, as dielectric, a liquid-crystallinemedium according to one or more of Claims 1 to 9.

The liquid-crystalline medium according to the invention preferably hasa nematic phase from ≦−20° C. to ≧70° C., particularly preferably from≦−30° C. to ≧80° C., very particularly preferably from ≦−40° C. to ≧90°C.

The expression “have a nematic phase” here means on the one hand that nosmectic phase and no crystallisation are observed at low temperatures atthe corresponding temperature and on the other hand that clearing stilldoes not occur on heating from the nematic phase. The investigation atlow temperatures is carried out in a flow viscometer at thecorresponding temperature and checked by storage in test cells having alayer thickness corresponding to the electro-optical use for at least100 hours. If the storage stability at a temperature of −20° C. in acorresponding test cell is 1000 h or more, the medium is referred to asstable at this temperature. At temperatures of −30° C. and −40° C., thecorresponding times are 500 h and 250 h respectively. At hightemperatures, the clearing point is measured by conventional methods incapillaries.

The liquid-crystal mixture preferably has a nematic phase range of atleast 60 K and a flow viscosity ν₂₀ of that most 30 mm²·s⁻¹ at 20° C.

The values of the birefringence Δn in the liquid-crystal mixture aregenerally between 0.07 and 0.16, preferably between 0.08 and 0.12.

The liquid-crystal mixture according to the invention has a Δ∈ of about−0.5 to −8.0, in particular of −3.0 to −6.0, where Δ∈ denotes thedielectric anisotropy. The rotational viscosity γ₁ at 20° C. ispreferably <165 mPa·s, in particular <140 mPa·s.

The liquid-crystal media according to the invention have relatively lowvalues for the threshold voltage (V₀). They are preferably in the rangefrom 1.7 V to 3.0 V, particularly preferably ≦2.75 V and veryparticularly preferably ≦2.4 V.

For the present invention, the term “threshold voltage” relates to thecapacitive threshold (V₀), also known as the Freedericksz threshold,unless explicitly indicated otherwise.

In addition, the liquid-crystal media according to the invention havehigh values for the voltage holding ratio, in particular after exposureto display backlights, in liquid-crystal cells.

In general, liquid-crystal media having a low addressing voltage orthreshold voltage exhibit a lower voltage holding ratio than thosehaving a greater addressing voltage or threshold voltage and vice versa.

For the present invention, the term “dielectrically positive compounds”denotes compounds having a Δ∈>1.5, the term “dielectrically neutralcompounds” denotes those having −1.5≦Δ∈≦1.5 and the term “dielectricallynegative compounds” denotes those having Δ∈<−1.5. The dielectricanisotropy of the compounds is determined here by dissolving 10% of thecompounds in a liquid-crystalline host and determining the capacitanceof the resultant mixture in at least one test cell in each case having alayer thickness of 20 μm with homeotropic and with homogeneous surfacealignment at 1 kHz. The measurement voltage is typically 0.5 V to 1.0 V,but is always lower than the capacitive threshold of the respectiveliquid-crystal mixture investigated.

The host mixture used for dielectrically positive and dielectricallyneutral compounds is ZLI-4792 and the host mixture used fordielectrically negative compounds is ZLI-2857, both from Merck KGaA,Germany. The values for the respective compounds to be investigated areobtained from the change in the dielectric constants of the host mixtureafter addition of the compound to be investigated and extrapolation to100% of the compound employed. 10% of the compound to be investigatedare dissolved in the host mixture. If the solubility of the substance istoo low for this, the concentration is halved in steps until theinvestigation can be carried out at the desired temperature.

All temperature values indicated for the present invention are in ° C.

The voltage holding ratio is determined in test cells produced at MerckKGaA. The measurement cells have soda-lime glass substrates and areprovided with polyimide alignment layers (polyimide AL 60702 from JSR).The layer thickness is uniformly 6.0 μm. The area of the transparent ITOelectrodes is 1 cm².

The mixtures according to the invention are suitable for all VA-TFTapplications, such as, for example, VAN, MVA, (S)—PVA and ASV. They arefurthermore suitable for IPS (in-plane switching), FFS (fringe fieldswitching) and PALC applications of negative Δ∈.

The nematic liquid-crystal mixtures in the displays according to theinvention generally comprise two components A and B, which themselvesconsist of one or more individual compounds.

Component A has significantly negative dielectric anisotropy and givesthe nematic phase a dielectric anisotropy of ≦−0.5. Besides one or morecompounds of the formulae IA, IB and/or IC, it preferably comprises thecompounds of the formulae IIA and/or IIB, furthermore compounds of theformula III.

The proportion of component A is preferably between 45 and 100%, inparticular between 60 and 100%.

For component A, one (or more) individual compound(s) which has (have) avalue of Δ∈≦−0.8 is (are) preferably selected. This value must be morenegative, the smaller the proportion A in the mixture as a whole.

Component B has pronounced nematogeneity and a flow viscosity of notgreater than 30 mm²·s⁻¹, preferably not greater than 25 mm²·s⁻¹, at 20°C.

Particularly preferred individual compounds in component B are extremelylow-viscosity nematic liquid crystals having a flow viscosity of notgreater than 18 mm²·s⁻¹, preferably not greater than 12 mm²·s⁻¹, at 20°C.

Component B is monotropically or enantiotropically nematic, has nosmectic phases and is able to prevent the occurrence of smectic phasesdown to very low temperatures in liquid-crystal mixtures. For example,if various materials of high nematogeneity are added to a smecticliquid-crystal mixture, the nematogeneity of these materials can becompared through the degree of suppression of smectic phases that isachieved.

A multiplicity of suitable materials is known to the person skilled inthe art from the literature. Particular preference is given to compoundsof the formula III.

In addition, these liquid-crystal phases may also comprise more than 18components, preferably 18 to 25 components.

The phases preferably comprise 4 to 15, in particular 5 to 12, andparticularly preferably <10, compounds of the formulae IA, IB and/or ICand compounds of the formulae IIA and/or IIB and optionally III.

Besides compounds of the formulae IA, IB, IC, and the compounds of theformulae IIA and/or IIB and optionally III, other constituents may alsobe present, for example in an amount of up to 45% of the mixture as awhole, but preferably up to 35%, in particular up to 10%.

The other constituents are preferably selected from nematic ornematogenic substances, in particular known substances, from the classesof the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenylor cyclohexyl benzoates, phenyl or cyclohexyl cyclo hexanecarboxylates,phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes,cyclohexylnaphthalenes, 1,4-biscyclohexylbiphenyls orcyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionallyhalogenated stilbenes, benzyl phenyl ethers, tolans and substitutedcinnamic acid esters.

The most important compounds which are suitable as constituents ofliquid-crystal phases of this type can be characterised by the formulaIVR⁹-L-G-E-R¹⁰  IVin which L and E each denote a carbo- or heterocyclic ring system fromthe group formed by 1,4-disubstituted benzene and cyclohexane rings,4,4′-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexanesystems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings,2,6-disubstituted naphthalene, di- and tetrahydronaphthalene,quinazoline and tetrahydroquinazoline,

-   G denotes —CH═CH— —N(O)═N—    -   —CH═CQ- —CH═N(O)—    -   —C≡C— —CH₂—CH₂—    -   —CO—O— —CH₂—O—    -   —CO—S— —CH₂—S—    -   —CH═N— —COO-Phe-COO—    -   —CF₂O— —CF═CF—    -   —OCF₂— —OCH₂—    -   —(CH₂)₄— —(CH₂)₃O—        or a C—C single bond, Q denotes halogen, preferably chlorine, or        —CN, and R⁹ and R¹⁹ each denote alkyl, alkenyl, alkoxy,        alkoxyalkyl or alkoxycarbonyloxy having up to 18, preferably up        to 8, carbon atoms, or one of these radicals alternatively        denotes CN, NC, NO₂, NCS, CF₃, SF₅, OCF₃, F, Cl or Br.

In most of these compounds, R⁹ and R¹⁹ are different from one another,one of these radicals usually being an alkyl or alkoxy group. Othervariants of the proposed substituents are also common. Many suchsubstances or also mixtures thereof are commercially available. Allthese substances can be prepared by methods known from the literature.

It goes without saying for the person skilled in the art that the VA,IPS, FFS or PALC mixture according to the invention may also comprisecompounds in which, for example, H, N, O, Cl and F have been replaced bythe corresponding isotopes.

Polymerisable compounds, so-called reactive mesogens (RMs), for exampleas disclosed in U.S. Pat. No. 6,861,107, may furthermore be added to themixtures according to the invention in concentrations of preferably0.12-5% by weight, particularly preferably 0.2-2%, based on the mixture.Mixtures of this type can be used for so-called polymer-stabilised VAmodes, in which polymerisation of the reactive mesogens is intended totake place in the liquid-crystalline mixture. The prerequisite for thisis that the liquid-crystal mixture does not itself comprise anypolymerisable components.

The construction of the liquid-crystal displays according to theinvention corresponds to the usual geometry, as described, for example,in EP-A 0 240 379.

The following examples are intended to explain the invention withoutlimiting it. Above and below, percent data denote percent by weight; alltemperatures are indicated in degrees Celsius.

Besides the compounds of the formulae IIA and/or IIB and one or morecompounds from the group of the compounds of the formulae IB, IC and ID,the mixtures according to the invention preferably comprise one or moreof the compounds indicated below.

The following abbreviations are used:

-   (n, m, z: each, independently of one another, 1, 2, 3, 4, 5 or 6)-   (O)C_(m)H_(2m+1) means OC_(m)H_(2m+1) or C_(m)H_(2m+1))

The liquid-crystal mixtures which can be used in accordance with theinvention are prepared in a manner which is conventional per se. Ingeneral, the desired amount of the components used in lesser amount isdissolved in the components making up the principal constituent,advantageously at elevated temperature. It is also possible to mixsolutions of the components in an organic solvent, for example inacetone, chloroform or methanol, and to remove the solvent again, forexample by distillation, after thorough mixing.

By means of suitable additives, the liquid-crystal phases according tothe invention can be modified in such a way that they can be employed inany type of, for example, ECB, VAN, IPS, GH or ASM-VA LCD display thathas been disclosed to date.

The dielectrics may also comprise further additives known to the personskilled in the art and described in the literature, such as, forexample, UV absorbers, antioxidants, nanoparticles and free-radicalscavengers. For example, 0-15% of pleochroic dyes, stabilisers or chiraldopants may be added.

For example, 0-15% of pleochroic dyes may be added, furthermoreconductive salts, preferably ethyldimethyldodecylammonium4-hexoxybenzoate, tetrabutylammonium tetraphenylboranate or complexsalts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq.Cryst. Volume 24, pages 249-258 (1973)), may be added in order toimprove the conductivity or substances may be added in order to modifythe dielectric anisotropy, the viscosity and/or the alignment of thenematic phases. Substances of this type are described, for example, inDE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430and 28 53 728.

Table A shows possible dopants which can be added to the mixturesaccording to the invention. If the mixtures comprise a dopant, it isemployed in amounts of 0.01-4% by weight, preferably 0.1-1.0% by weight.

TABLE A

C 15

CB 15

CM 21

R/S-811

CM 44

CM 45

CM 47

CN

R/S-1011

R/S-2011

R/S-3011

R/S-4011

R/S-5011

Stabilisers which can be added, for example, to the mixtures accordingto the invention in amounts of up to 10% by weight, based on the totalamount of the mixture, preferably 0.01 to 6% by weight, in particular0.1 to 3% by weight, are shown below in Table B.

TABLE B

(n = 1-12)

The following examples are intended to explain the invention withoutlimiting it. Above and below,

-   V_(o) denotes the threshold voltage, capacitive [V] at 20° C.-   Δn denotes the optical anisotropy measured at 20° C. and 589 nm-   Δ∈ denotes the dielectric anisotropy at 20° C. and 1 kHz-   cl.p. denotes the clearing point [° C.]-   K₁ denotes the elastic constant, “splay” deformation at 20° C. [pN]-   K₃ denotes the elastic constant, “bend” deformation at 20° C. [pN]-   γ₁ denotes the rotational viscosity measured at 20° C. [mPa·s],    determined by the rotation method in a magnetic field-   LTS denotes the low-temperature stability (nematic phase),    determined in test cells-   VHR (20) denotes the voltage holding ratio at 20° C. [%]-   VHR (100) denotes the voltage holding ratio after 5 min. at 100° C.    [%]-   VHR (BL) denotes the voltage holding ratio after backlight* exposure    [%]-   VHR (100, BL) voltage holding ratio after backlight* exposure and    after 5 min. at 100° C. [%]    -   *commercial CCFL (cold cathode fluorescent lamp) backlight

The display used for measurement of the threshold voltage has twoplane-parallel outer plates at a separation of 20 μm and electrodelayers with overlying alignment layers of SE-1211 (Nissan Chemicals) onthe insides of the outer plates, which effect a homeotropic alignment ofthe liquid crystals.

All concentrations in this application relate to the correspondingmixture or mixture component, unless explicitly indicated otherwise. Allphysical properties are determined as described in “Merck LiquidCrystals, Physical Properties of Liquid Crystals”, status November 1997,Merck KGaA, Germany, and apply for a temperature of 20° C., unlessexplicitly indicated otherwise.

MIXTURE EXAMPLES Example 1

CY-3-O4 9.60% Clearing point [° C.]: 63 CY-5-O4 9.60% Δn [589 nm, 20°C.]: 0.0762 CCY-2-O2 9.60% Δε [1 kHz, 20° C.]: −3.0 CCY-3-O2 9.60% γ₁[mPa · s, 20° C.]: 112 CCY-5-O2 6.40% CCY-2-1 9.60% CCY-3-1 6.40% CC-5-V6.40% PCH-53 12.80% CC-1-V3 20.00%

Example 2

CY-3-O4 9.60% Clearing point [° C.]: 78 CY-5-O4 9.60% Δn [589 nm, 20°C.]: 0.0820 CCY-2-O2 9.60% Δε [1 kHz, 20° C.]: −3.1 CCY-3-O2 9.60% γ₁[mPa · s, 20° C.]: 140 CCY-5-O2 6.40% CCY-2-1 9.60% CCY-3-1 6.40% CC-5-V6.40% PCH-53 12.80% CC-5-V3 20.00%

Example 3

CY-3-O4 9.60% Clearing point [° C.]: 75 CY-5-O4 9.60% Δn [589 nm, 20°C.]: 0.0780 CCY-2-O2 9.60% Δε [1 kHz, 20° C.]: −3.3 CCY-3-O2 9.60% γ₁[mPa · s, 20° C.]: 125 CCY-5-O2 6.40% CCY-2-1 9.60% CCY-3-1 6.40% CC-5-V6.40% PCH-53 12.80% CC-4-V2 20.00%

Example 4

CY-3-O2 15.00% Clearing point [° C.]: 79.5 CY-5-O2 14.00% Δn [589 nm,20° C.]: 0.0829 CCY-3-O2 10.00% ε_(∥) [1 kHz, 20° C.]: 3.5 CCY-3-O310.00% ε_(⊥) [1 kHz, 20° C.]: 7.3 CCY-4-O2 5.00% Δε [1 kHz, 20° C.]:−3.7 CPY-3-O2 8.00% K₁ [pN, 20° C.]: 14.7 CC-3-V1 10.00% K₃ [pN, 20°C.]: 15.4 CCH-34 10.00% K₁/K₃ [20° C.]: 1.05 CCH-35 3.00% V₀ [V, 20°C.]: 2.14 CCH-301 5.00% γ₁ [mPa · s, 20° C.]: 114 CC-4-V2 10.00% LTScells −20° C. >1000 h LTS cells −30° C. >1000 h LTS bulk −20° C. >1000 h

Example 5

CY-3-O2 13.00% Clearing point [° C.]: 80 CY-5-O2 12.00% Δn [589 nm, 20°C.]: 0.035 CCY-3-O2 10.00% ε_(∥) [1 kHz, 20° C.]: 3.5 CCY-3-O3 11.00%ε_(⊥) [1 kHz, 20° C.]: 7.2 CCY-4-O2 8.00% Δε [1 kHz, 20° C.]: −3.7CPY-3-O2 8.00% K₁ [pN, 20° C.]: 15.0 CC-3-V1 10.00% K₃ [pN, 20° C.]:16.1 CCH-34 10.00% K₁/K₃ [20° C.]: 1.07 CCH-35 3.00% V₀ [V, 20° C.]:2.20 CCH-301 5.00% γ₁ [mPa · s, 20° C.]: 119 CC-1-V3 10.00% LTS cells−20° C. >1000 h LTS bulk −20° C. >1000 h

Example 6

CY-3-O2 15.00% Clearing point [° C.]: 80 CY-5-O2 15.00% Δn [589 nm, 20°C.]: 0.0821 CCY-3-O2 10.00% ε_(∥) [1 kHz, 20° C.]: 3.5 CCY-3-O3 10.00%ε_(⊥) [1 kHz, 20° C.]: 7.3 CCY-4-O2 6.00% Δε [1 kHz, 20° C.]: −3.8CPY-3-O2 6.00% K₁ [pN, 20° C.]: 15.3 CC-3-V1 10.00% K₃ [pN, 20° C.]:16.2 CCH-34 10.00% K₁/K₃ [20° C.]: 1.06 CCH-35 3.00% V₀ [V, 20° C.]:2.19 CCH-301 5.00% γ₁ [mPa · s, 20° C.]: 120 CC-5-V3 10.00% LTS cells−20° C. >1000 h

Example 7

CY-3-O2 13.00% Clearing point [° C.]: 79.5 CY-5-O2 14.00% Δn [589 nm,20° C.]: 0.0835 CCY-3-O2 10.00% ε_(∥) [1 kHz, 20° C.]: 3.5 CCY-3-O310.00% ε_(⊥) [1 kHz, 20° C.]: 7.2 CCY-4-O2 6.00% Δε [1 kHz, 20° C.]:−3.7 CPY-3-O2 9.00% K₁ [pN, 20° C.]: 14.7 CC-3-V1 10.00% K₃ [pN, 20°C.]: 15.4 CCH-34 10.00% K₁/K₃ [20° C.]: 1.05 CCH-35 3.00% V₀ [V, 20°C.]: 2.16 CCH-301 5.00% γ₁ [mPa · s, 20° C.]: 1000 CC-2-V3 10.00% LTScells −20° C. >1000 h LTS cells −30° C. >1000 h LTS cells −40° C. >1000h LTS bulk −20° C. >1000 h

Example 8

CY-3-O2 18.00% Clearing point [° C.]: 80 CY-5-O2 10.00% Δn [589 nm, 20°C.]: 0.0837 CCY-3-O2 10.00% ε_(∥) [589 nm, 20° C.]: 4.6 CCY-3-O3 10.00%ε_(⊥) [589 nm, 20° C.]: 6.9 CCY-4-O2 6.00% Δε [589 nm, 20° C.]: −2.3CPY-3-O2 8.00% K₁ [pN, 20° C.]: 16.5 CC-3-V1 10.00% K₃ [pN, 20° C.]:15.3 CCH-34 10.00% K₁/K₃ [20° C.]: 0.93 CCH-35 3.00% V₀ [V, 20° C.]:2.74 CCH-301 5.00% γ₁ [mPa · s, 20° C.]: 118 CC-3-V2 10.00% LTS cells−20° C. >1000 h LTS bulk −20° C. >1000 h

Example 9

CY-3-O2 14.00% Clearing point [° C.]: 79 CY-5-O2 15.00% Δn [589 nm, 20°C.]: 0.0830 CCY-3-O2 10.00% ε_(∥) [589 nm, 20° C.]: 3.5 CCY-3-O3 10.00%ε_(⊥) [589 nm, 20° C.]: 7.1 CCY-4-O2 4.00% Δε [589 nm, 20° C.]: −3.6CPY-3-O2 8.00% K₁ [pN, 20° C.]: 14.7 CC-3-V1 10.00% K₃ [pN, 20° C.]:15.7 CCH-34 10.00% K₁/K₃ [20° C.]: 1.07 CCH-35 4.00% V₀ [V, 20° C.]:2.19 CCH-301 5.00% γ₁ [mPa · s, 20° C.]: 109 CC-2V-V2 10.00% LTS cells−20° C. >1000 h LTS cells −30° C. >1000 h

Example 10

CY-3-O4 10.00% Clearing point [° C.]: 79 CY-5-O2 15.00% Δn [589 nm, 20°C.]: 0.0940 CCY-3-O3 8.00% ε_(∥) [589 nm, 20° C.]: 3.3 PYP-2-3 7.00%ε_(⊥) [589 nm, 20° C.]: 6.3 CLY-2-O4 6.00% Δε [589 nm, 20° C.]: −3.0CLY-3-O2 6.00% K₁ [pN, 20° C.]: 15.8 CLY-3-O3 6.00% K₃ [pN, 20° C.]:14.2 CC-3-V1 11.00% K₁/K₃ [20° C.]: 0.90 CCP-31 6.00% V₀ [V, 20° C.]:2.30 CC-4-V2 13.00% γ₁ [mPa · s, 20° C.] 118 CCH-34 6.00% PCH-53 6.00%

Example 11

CY-3-O4 10.00% Clearing point [° C.]: 80 CY-5-O2 15.00% Δn [589 nm, 20°C.]: 0.0847 CCY-3-O3 8.00% ε_(∥) [589 nm, 20° C.]: 3.4 CCY-4-O2 6.00%ε_(⊥) [589 nm, 20° C.]: 6.4 CPY-2-O2 8.00% Δε [589 nm, 20° C.]: −3.1CPY-3-O2 8.00% K₁ [pN, 20° C.]: 15.0 PYP-2-3 3.00% K₃ [pN, 20° C.]: 14.2CC-3-V1 12.00% K₁/K₃ [20° C.]: 0.95 CCP-31 5.00% V₀ [V, 20° C.]: 2.26CC-4-V2 15.00% γ₁ [mPa · s, 20° C.]: 120 CCH-34 5.00% LTS cells −20°C. >1000 h PCH-53 5.00% LTS cells −30° C. >1000 h LTS cells −40°C. >1000 h LTS bulk −20° C. >1000 h

Example 12

CY-3-O4 14.00% Clearing point [° C.]: 80.5 CY-5-O2 14.00% Δn [589 nm,20° C.]: 0.0937 CCY-3-O3 8.00% ε_(∥) [589 nm, 20° C.]: 3.4 CCY-4-O23.00% ε_(⊥) [589 nm, 20° C.]: 6.5 CPY-2-O2 9.00% Δε [589 nm, 20° C.]:−3.1 CPY-3-O2 8.00% K₁ [pN, 20° C.]: 14.7 CC-3-V1 10.00% K₃ [pN, 20°C.]: 14.5 CCP-2V-1 12.00% K₁/K₃ [20° C.]: 0.99 CC-4-V2 10.00% V₀ [V, 20°C.]: 2.29 CCH-34 6.00% γ₁ [mPa · s, 20° C.]: 126 PCH-53 6.00% LTS cells−20° C. >1000 h LTS cells −30° C. >1000 h LTS cells −40° C. >1000 h

Example 13

CY-3-O4 27.00% Clearing point [° C.]: 81 CY-5-O2 8.00% Δn [589 nm, 20°C.]: 0.0945 CCY-3-O3 4.00% ε_(∥) [589 nm, 20° C.]: 3.4 CPY-2-O2 8.00%ε_(⊥) [589 nm, 20° C.]: 6.6 CPY-3-O2 9.00% Δε [589 nm, 20° C.]: −3.2CC-3-V1 9.00% K₁ [pN, 20° C.]: 15.1 CCP-2V-1 10.00% K₃ [pN, 20° C.]:15.5 CCP-3V-1 9.00% K₁/K₃ [20° C.]: 1.03 CCH-34 12.00% V₀ [V, 20° C.]:2.32 PCH-53 4.00% γ₁ [mPa · s, 20° C.]: 132 LTS cells −20° C. >1000 hLTS cells −30° C. >1000 h LTS bulk −20° C. >1000 h

Example 14

CY-3-O4 20.00% Clearing point [° C.]: 80.5 CY-5-O2 11.00% Δn [589 nm,20° C.]: 0.0938 CCY-3-O3 5.00% ε_(∥) [589 nm, 20° C.]: 3.4 CPY-2-O210.00% ε_(⊥) [589 nm, 20° C.]: 6.5 CPY-3-O2 10.00% Δε [589 nm, 20° C.]:−3.1 CC-3-V1 10.00% K₁ [pN, 20° C.]: 15.0 CCP-3V-1 12.00% K₃ [pN, 20°C.]: 14.4 CC-4-V2 12.00% K₁/K₃ [20° C.]: 0.96 CCH-34 10.00% V₀ [V, 20°C.]: 2.27 γ₁ [mPa · s, 20° C.]: 121 LTS cells −20° C. >1000 h

Example 15

CY-3-O4 18.00% Clearing point [° C.]: 79.5 CY-5-O2 10.00% Δn [589 nm,20° C.]: 0.0977 CCY-3-O3 8.00% ε_(∥) [589 nm, 20° C.]: 3.4 CPY-2-O210.00% ε_(⊥) [589 nm, 20° C.]: 6.5 CPY-3-O2 10.00% Δε [589 nm, 20° C.]:−3.1 CC-3-V1 11.00% K₁ [pN, 20° C.]: 14.6 CCP-1V-1 12.00% K₃ [pN, 20°C.]: 15.8 CC-4-V2 8.00% K₁/K₃ [20° C.]: 1.08 CCH-34 6.00% V₀ [V, 20°C.]: 2.37 PCH-53 7.00% γ₁ [mPa · s, 20° C.]: 127 LTS cells −20° C. >1000h VHR (100, BL) LTS cells −30° C. >1000 h  0 h 96.7% LTS cells −40°C. >1000 h 168 h 88.0% LTS bulk −20° C. >1000 h 500 h 77.9%

Comparative Example 1

CY-3-O4 30.00% Clearing point [° C.]: 80 CY-5-O4 5.00% Δn [589 nm, 20°C.]: 0.0946 CCY-3-O3 4.00% ε_(∥) [589 nm, 20° C.]: 3.4 CPY-2-O2 8.00%ε_(⊥) [589 nm, 20° C.]: 6.5 CPY-3-O2 8.00% Δε [589 nm, 20° C.]: −3.1CC-3-V1 10.00% K₁ [pN, 20° C.]: 14.2 CCP-V-1 12.00% K₃ [pN, 20° C.]:15.2 CCP-V2-1 12.00% K₁/K₃ [20° C.]: 1.07 CCH-34 11.00% V₀ [V, 20° C.]:2.33 γ₁ [mPa · s, 20° C.]: 127 VHR (100, BL) LTS cells −30° C. 384  0 h98.3% 168 h 78.0% 500 h 67.7%

Example 16

CY-3-O4 14.00% Clearing point [° C.]: 81.5 CY-5-O2 15.00% Δn [589 nm,20° C.]: 0.0953 CCY-3-O3 8.00% ε_(∥) [589 nm, 20° C.]: 3.4 CCY-4-O23.00% ε_(⊥) [589 nm, 20° C.]: 6.7 CPY-2-O2 9.00% Δε [589 nm, 20° C.]:−3.3 CPY-3-O2 9.00% K₁ [pN, 20° C.]: 15.2 CC-3-V1 10.00% K₃ [pN, 20°C.]: 15.0 CCP-31 6.00% K₁/K₃ [20° C.]: 0.99 CCP-33 7.00% V₀ [V, 20° C.]:2.26 CC-4-V2 10.00% γ₁ [mPa · s, 20° C.]: 135 CCH-34 4.00% LTS cells−20° C. >1000 h PCH-53 5.00% LTS cells −30° C. >1000 h LTS cells −40°C. >1000 h VHR (100, BL) LTS bulk −20° C. >1000 h  0 h 97.0% 168 h 87.1%500 h 74.5%

Example 17

CY-3-O4 10.00% Clearing point [° C.]: 79.5 CY-5-O2 15.00% Δn [589 nm,20° C.]: 0.0949 CCY-3-O3 9.00% ε_(∥) [589 nm, 20° C.]: 3.4 CCY-4-O28.00% ε_(⊥) [589 nm, 20° C.]: 6.7 CPY-2-O2 8.00% Δε [589 nm, 20° C.]:−3.3 CPY-3-O2 7.00% K₁ [pN, 20° C.] 15.0 PYP-2-3 3.00% K₃ [pN, 20° C.]14.4 CC-3-V1 11.00% K₁/K₃ [20° C.] 0.96 CCP-31 5.00% V₀ [V, 20° C.] 2.22CC-4-V2 10.00% γ₁ [mPa · s, 20° C.]: 127 CCH-34 7.00% LTS cells −20°C. >1000 h PCH-53 7.00% LTS cells −30° C. >1000 h LTS cells −40°C. >1000 h VHR (100, BL) LTS bulk −20° C. >1000 h  0 h 96.9% 168 h 88.8%500 h 77.7%

Example 18

CY-3-O4 12.00% Clearing point [° C.]: 74.5 CY-5-O4 12.00% Δn [589 nm,20° C.]: 0.084 CCY-2-O2 12.00% Δε [1 kHz, 20° C.]: −4.0 CCY-3-O2 12.00%CCY-5-O2 8.00% CCY-2-1 12.00% CCY-3-1 8.00% CC-5-V 8.00% PCH-53 16.00%

In each case, 20% of one of the individual substances mentioned underV18 a-i are incorporated into the host indicated above, and the VHR(100) [%] after exposure to a backlight is measured:

Exposure duration [h] 0 330 500 References CC-3-V 98.5 77.0 72.3 CC-5-V98.4 77.6 73.0 V18 a CC-4-V2 98.8 86.5 84.2 V18 b CC-2-V3 98.6 89.6 84.5V18 c CC-1-V3 98.8 87.8 83.3 V18 d CC-2V-V2 98.6 86.9 82.6 V18 e CC-3-V298.7 89.2 84.4 Reference CCP-V-1 98.5 77.0 72.3 V18 f CCP-2V-1 98.4 84.576.9 V18 g CCP-3V-1 98.1 86.0 80.0 V18 h CCP-4V-1 97.7 90.3 87.7 V18 iCCP-1V-2 98.2 88.4 85.1

The table shows that the compounds of the formulae IA, IB and IC exhibita higher voltage holding ratio in the host after backlight exposure thanthe reference substances.

1. A liquid-crystalline medium, comprising at least one of the followingcompounds

in which R^(2A) and R^(2C) each, independently of one another, denote analkyl radical having up to 6 C atoms which is unsubstituted,monosubstituted by CN or CF₃ or at least monosubstituted by halogen, inwhich one or more CH₂ groups may be replaced by —O—, —S—,

—C≡C—, —CF₂O—, —OCF₂—, —OC—O— or —O—CO— in such a way that O atoms arenot linked directly to one another, and, if L=F, R^(2C) may also denotehalogen, and L denotes H or F.
 2. A liquid-crystalline medium accordingto claim 1, further comprising one or more compounds of formulae IIAand/or IIB

in which R² denotes an alkyl or alkenyl radical having up to 15 C atomswhich is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen, in which one or more CH₂ groups may bereplaced by —O—, —S—,

—C═C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms arenot linked directly to one another, L¹⁻⁴ each, independently of oneanother, denote F or Cl, Z² and Z^(2′) each, independently of oneanother, denote a single bond, —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—,—CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —CF═CF—, or —CH═CHCH₂O—, P denotes1 or 2, and v denotes 1 to
 6. 3. A liquid-crystalline medium accordingto claim 1, further comprising one or more compounds of formula III

in which R³¹ and R³² each, independently of one another, denote astraight-chain alkyl, alkoxyalkyl or alkoxy radical having up to 12 Catoms, and

Z³ denotes a single bond, —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—,—OCH₂—, —COO—, —OCO—, —C₂F₄—, —C₄H₉—, or —CF═CF—.
 4. Aliquid-crystalline medium according to claim 1, further comprising oneor more compounds of the following formulae

in which R⁷⁻¹⁰ each, independently of one another, denotes an alkyl oralkenyl radical having up to 15 C atoms which is unsubstituted,monosubstituted by CN or CF₃ or at least monosubstituted by halogen, inwhich one or more CH₂ groups may be replaced by —O—, —S—,

—C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms arenot linked directly to one another, and w and x each, independently ofone another, denote 1 to
 6. 5. A liquid-crystalline medium according toclaim 1, further comprising one or more terphenyls of formulae T-1 toT-21

in which R denotes a straight-chain alkyl or alkoxy radical having 1-7 Catoms, and m denotes 1-6.
 6. A liquid-crystalline medium according toclaim 1, further comprising one or more compounds of formulae O-1 toO-14

in which R¹ and R² each, independently of one another, denote an alkylradical having up to 6 C atoms which is unsubstituted, monosubstitutedby CN or CF₃ or at least monosubstituted by halogen, in which one ormore CH₂ groups may be replaced by —O—, —S—,

—C≡C—, —CF₂O—, —OCF₂—, —OC—O— or —O—CO— in such a way that O atoms arenot linked directly to one another.
 7. A liquid-crystalline mediumaccording to claim 1, further comprising one or more indane compounds offormula In

in which R¹¹, R¹², R¹³ denote a straight-chain alkyl or alkoxy,alkoxyalkyl or alkenyl radical having 1-5 C atoms, R¹² and R¹³additionally denote halogen,

and i denotes 0, 1 or
 2. 8. A liquid-crystalline medium according toclaim 1, wherein the proportion of the compounds of the formulae IA-1,IA-2, IA-3, IB-1, IB-2, IB-3, IB-4, IB-5, IB-6, IB-7, IC-1, IC-2 andIC-3 in the medium as a whole is ≧5% by weight.
 9. A process forpreparing a liquid-crystalline medium according to claim 1, comprisingmixing together at least one compound of formulae IA-1, IA-2, IA-3,IB-1, IB-2, IB-3, IB-4, IB-5, IB-6, IB-7, IC-1, IC-2 and IC-3 with atleast one further liquid-crystalline compound.
 10. An electro-opticaldisplay comprising the liquid-crystalline medium according to claim 1.11. An electro-optical display having active-matrix addressing,containing, as dielectric, a liquid-crystalline medium according toclaim
 1. 12. An electro-optical display according to claim 11, which isan ECB, PALC, FFS or IPS display.
 13. A liquid-crystalline mediumaccording to claim 1, further comprising one or more indane compounds offormulae In-1 to IN-16

in which R¹¹ denotes a straight-chain alkyl or alkoxy, alkoxyalkyl oralkenyl radical having 1-5 C atoms.
 14. A liquid-crystalline mediumaccording to claim 1, further comprising one or more indane compounds offormula In

in which R¹¹, R¹², R¹³ denote a straight-chain alkyl or alkoxy,alkoxyalkyl or alkenyl radical having 1-5 C atoms, R¹² and R¹³additionally denote halogen or hydrogen,

and i denotes 0, 1 or
 2. 15. A liquid-crystalline medium according toclaim 1, which comprises at least one compound of formulae IC-1 to IC-3wherein L denotes F.
 16. A liquid-crystalline medium according to claim1, which comprises at least one compound of formulae IB-1 to IB-7.
 17. Aliquid-crystalline medium according to claim 1, which comprises at leastone compound of formulae IC-1 to IC-3.
 18. A liquid-crystalline mediumaccording to claim 1, which comprises at least one compound of formulaeIA-1a to IA-3d.
 19. A liquid-crystalline medium according to claim 1,which comprises at least one compound of formulae IA-2a to IA-3d.
 20. Amethod for reducing image sticking in a display, comprising adding aliquid-crystalline medium according to claim 1 into said display.